Dynamical properties at Voter critical points*

We discuss the dynamical properties of two non-equilibrium systems that exhibit a critical point belonging to the Voter universality class. At a Voter critical point an order-disorder transition and an absorbing transition take place at the same time. Our extensive numerical simulations reveal  a simple aging scaling behavior of two-time quantities with universal dynamic exponents. This corrects earlier claims in the literature. The properties of the time-dependent magnetization at the critical point depend on whether the model is linear or non-linear.